U.S. patent application number 13/210622 was filed with the patent office on 2011-11-24 for method of manufacturing a light emitting device.
Invention is credited to ANTHONY J. NICHOL.
Application Number | 20110286234 13/210622 |
Document ID | / |
Family ID | 40549515 |
Filed Date | 2011-11-24 |
United States Patent
Application |
20110286234 |
Kind Code |
A1 |
NICHOL; ANTHONY J. |
November 24, 2011 |
METHOD OF MANUFACTURING A LIGHT EMITTING DEVICE
Abstract
A method of manufacturing a light emitting device includes
separating a plurality of regions in a film with a thickness not
greater than 0.5 millimeters to form a plurality of legs continuous
with a body of film, folding the plurality of legs such that each
leg terminates in a stack of bounding edges, disposing the stack of
bounding edges proximate at least one light source such that light
from the at least one light source propagates through the legs and
the body by total internal reflection, and treating the film to
form a plurality of light scattering features therein such that
frustrated totally internally reflected light exits the light
emitting device at a visible light emitting area and the light
emitting area is at most barely visible when not illuminated by the
at least one light source.
Inventors: |
NICHOL; ANTHONY J.;
(Chicago, IL) |
Family ID: |
40549515 |
Appl. No.: |
13/210622 |
Filed: |
August 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12682387 |
Apr 9, 2010 |
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PCT/US08/79041 |
Oct 7, 2008 |
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13210622 |
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60978755 |
Oct 9, 2007 |
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Current U.S.
Class: |
362/560 ; 29/428;
29/460 |
Current CPC
Class: |
Y10T 29/49888 20150115;
G02B 6/0076 20130101; Y10S 362/812 20130101; G02B 6/0018 20130101;
Y10T 29/49826 20150115 |
Class at
Publication: |
362/560 ; 29/428;
29/460 |
International
Class: |
G01D 11/28 20060101
G01D011/28; B23P 11/00 20060101 B23P011/00; B23P 19/04 20060101
B23P019/04; F21V 8/00 20060101 F21V008/00 |
Claims
1. A method of manufacturing a sign, said method comprising:
separating a plurality of regions in a film with a thickness not
greater than 0.5 millimeters to form a plurality of lightguide legs
continuous with a body of the film, the legs having internally
light reflecting, optically smooth, lateral edges; folding the
plurality of legs such that each leg terminates in a stack of
bounding edges; disposing the stack of bounding edges proximate at
least one light source such that light from the at least one light
source propagates through the legs and the body by total internal
reflection; treating a surface of the body of the film to form a
plurality of light scattering features on the surface such that:
the light scattering features frustrate totally internally
reflected light from the at least one light source propagating
through the legs and the body; the frustrated totally internally
reflected light exits the sign at a visible light emitting area;
and the light scattering features do not appreciably change an
appearance of a window when the sign is disposed adjacent the
window and the at least one light source is not emitting light.
2. The method of claim 1 wherein the plurality of legs are folded
over each other.
3. The method of claim 1 wherein the light propagating through each
leg combines within the body of the film.
4. The method of claim 1 wherein the at least one light source
comprises a plurality of light emitting diodes wherein light from
each light emitting diode combines within each leg.
5. The method of claim 1 wherein the at least one light source
comprises at least two light emitting diodes wherein the light from
the at least two light emitting diodes combines within the body of
the film.
6. The method of claim 1 further comprising adding a cladding layer
to the film.
7. The method of claim 1 wherein the window is in a door.
8. The method of claim 1 wherein the window is in the front of a
refrigeration device.
9. A method of manufacturing a light emitting device, said method
comprising: separating a plurality of regions in a film with a
thickness not greater than 0.5 millimeters to form a plurality of
legs continuous with a body of film; folding the plurality of legs
such that each leg terminates in a stack of bounding edges;
disposing the stack of bounding edges proximate at least one light
source such that light from the at least one light source
propagates through the legs and the body by total internal
reflection; and treating the film to form a plurality of light
scattering features therein such that: the light scattering
features frustrate totally internally reflected light from the at
least one light source propagating through the legs and within the
body; the frustrated totally internally reflected light exits the
light emitting device at a visible light emitting area; and the
light emitting area is at most barely visible when not illuminated
by the at least one light source.
10. The method of claim 9 wherein the plurality of legs are folded
over each other.
11. The method of claim 9 wherein light from each leg combines
within the body of the film.
12. The method of claim 9 wherein the at least one light source
comprises a plurality of light emitting diodes, wherein light from
each light emitting diode combines within each leg.
13. The method of claim 12 wherein the light from the plurality of
light emitting diodes combines within the body.
14. The method of claim 9 wherein treating the film comprises
printing a light scattering ink on a surface of the film.
15. The method of claim 9 further comprising disposing the light
emitting area substantially adjacent a window.
16. The method of claim 9 further comprising disposing the light
emitting area in front of a refrigeration device.
17. A method of displaying a light emitting device, said method
comprising: providing a light emitting device comprising a
film-based lightguide with a thickness not greater than 0.5
millimeters and with having lightguide legs continuous with a body
of the lightguide, the legs are folded, stacked, and disposed to
receive light emitted from at least one light source and transmit
the light through the legs and into the lightguide by total
internal reflection, wherein the light exits the light emitting
device in light emitting areas of the lightguide due to frustrated
total internal reflection from light scattering features; and
disposing the light emitting device in front of an object such that
the light emitting device does not appreciably change an appearance
of the object when looking through the light emitting areas of the
light emitting device when the at least one light source is not
emitting light.
18. The method of claim 17 wherein the object is a window.
19. The method of claim 17 wherein the object is a refrigeration
device.
20. The method of claim 17 wherein the object is a wall.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/682,387, filed Apr. 9, 2010 from PCT International
Application No. PCT/US08/79041 filed Oct. 7, 2008, which claims the
benefit of U.S. Provisional Patent Application 60/978,755, filed
Oct. 9, 2007, the entirety of which is incorporated by reference
herein.
BACKGROUND
[0002] This document concerns an invention relating generally to
lightguides such as fiberoptic cable and edge-lit films, and more
specifically to devices and methods for providing edge-lighting for
films with high efficiency.
[0003] There are numerous forms of lightguides, with perhaps the
most common being the optical fiber, which is typically formed as a
clear glass or plastic cylinder with a diameter of 1 micrometer to
5 mm. A light source is coupled to an end of the optical fiber, and
is transmitted through its length, typically with the intent of
delivering as much of the light as possible to the opposite end of
the optical fiber. Some of the light is lost along the length of
the optical fiber owing to light absorption and light scattering
(i.e., light escaping through the surface of the fiber). However,
with the choice of appropriate materials and manufacturing
processes, absorption and scattering losses can be minimized. For
example, whereas an optical fiber formed of plastic (e.g.,
polymethyl methacrylate or PMMA) typically has an attenuation of
less than 0.2 dB per meter, an optical fiber formed of high-grade
fused silica typically has an attenuation of less than 0.01 dB per
meter. Plastic lightguides tend to have greater losses, and thus
tend to be used only in circumstances where light only needs to be
transmitted short distances. Scattering can also be reduced by
forming an optical fiber with a core having a higher refractive
index, and an outer layer having a lower refractive index, so that
light received by the core experiences internal reflection (i.e.,
it reflects from the boundary between the core and the outer layer
and continues to travel along the fiber, rather than being
transmitted from the core to the outer layer and its surroundings).
Efficient light transfer is also enhanced if the light source is
coupled to the end of the optical fiber with high efficiency so
that the greatest possible amount of light from the light source is
transmitted into the fiber. Good coupling efficiency can be
achieved by (for example) treating the end of the optical fiber to
be as smooth and transparent as possible, thereby better allowing
the light to be transferred into the end of the fiber rather than
being reflected therefrom, and by transmitting the light from the
light source to the fiber using an optical coupling gel matched to
the refractive index of the fiber.
[0004] Another form of lightguide is a transparent plate which has
a light source coupled to one edge. This arrangement is often
referred to as "edge-lighting," and it typically requires plates
with thicknesses greater than 2 mm to achieve effective coupling
from typical light sources such as light emitting diodes (LEDs) and
halogen, incandescent, metal halide or xenon lamps. The surface of
a plate may be treated at certain areas, as by surface roughening,
etching, or the addition of a material that promotes light
scattering (e.g., white paint), to reduce or defeat internal
reflection at these areas to cause light emission from the plate at
these or adjacent areas. As a result, the treated areas appear to
glow. Because the plates typically do not efficiently receive or
transmit light, and have higher losses along their lengths, the
treated areas must often be functionally graded (i.e., they must
generate lesser scattering near the light source and greater
scattering farther from the light source) if the treated areas are
to appear to have uniform illumination.
[0005] The plates are typically rigid, having very limited
flexibility, though in some cases flexible plastic films are used
(typically having a thickness of 0.5 mm or so). However, these are
rarely used because it is difficult to efficiently couple light
into such films at low cost. Most light sources have dimensions
greater than millimeters, with the films having much smaller
thicknesses for receiving the input light, so it is difficult to
efficiently and inexpensively channel the majority of the light
source's light output into the edge of the film. One solution to
this problem is presented in U.S. Pat. No. 7,237,396, wherein a
light source is coupled to the first ends of a bunched bundle of
optical fibers, and the second ends are spread along an edge of the
film to effectively provide an array of input light sources. The
drawback of this approach is that it can be time-consuming and
difficult to achieve: for efficient coupling, the second ends of
the fibers must be precisely aligned with the edge of the film;
treatment of the fiber ends and film edge to reduce scatting is
time-consuming; and similarly the assembly demands of the system
(which preferably uses optical coupling gel at the various optical
interfaces) are high. There are also losses at the interface
between the light source and the bundle, since the spaces between
the fibers in the bundle create a loss. It would therefore be
advantageous to have devices and methods available for
high-efficiency coupling of light sources to films and plates with
lower cost and ease of manufacture and assembly.
SUMMARY
[0006] The invention, which is defined by the claims set forth at
the end of this document, is directed to devices and methods which
at least partially alleviate the aforementioned problems. A basic
understanding of some of the features of preferred versions of the
invention can be attained from a review of the following brief
summary of the invention, with more details being provided
elsewhere in this document. To assist in the reader's
understanding, the following review makes reference to the
accompanying drawings (which are briefly reviewed in the "Brief
Description of the Drawings" section following this Summary section
of this document).
[0007] Referring to FIGS. 1A-1C for a schematic view of an
exemplary version of the invention, a flexible sheet 100 of at
least partially translucent material is surrounded by a bounding
edge 102 (see particularly FIG. 1A). The sheet 100 is folded upon
itself--here twice, once in FIG. 1B and once in FIG. 1C--such that
portions 102A, 102B, 102C, 102D, 102E, 102F of the bounding edge
102 overlap, and an unfolded portion 104 (a "body") is left where
the sheet 100 is not folded upon itself. In this example, the sheet
100 is formed with a number of discrete legs 106 extending from the
unfolded portion/body 104, and the legs 106 each terminate at the
portions 102A, 102B, 102C, 102D, 102E, 102F of the bounding edge
102 which are to overlap. The legs 106 are folded between their
bounding edges 102A, 102B, 102C, 102D, 102E, 102F and the body 104
at folds 108 (as seen in FIG. 1B, as well as in FIG. 1C) such that
at least some of the legs 106 are bent into stacked relationship,
with their bounding edges 102A, 102B, 102C, 102D, 102E, 102F
preferably being at least substantially aligned, and also being
prepared to define an at least substantially smooth and continuous
surface (e.g. by polishing). One or more light sources 110 can then
be situated to illuminate the adjacently situated bounding edges
102A, 102B, 102C, 102D, 102E, 102F of the stacked legs 106. The
light is received by the overlapping edges 102A, 102B, 102C, 102D,
102E, 102F, which inherently provide an area greater than the
thickness of the sheet 100 so that the sheet 100 (the stacked edges
102A, 102B, 102C, 102D, 102E, 102F) more efficiently receive a
greater amount of light from the light source 110. The received
light is transmitted through the sheet 100 via internal reflection
such that the unfolded portion/body 104 is internally illuminated.
To enhance such internal reflection, the sheet 100 preferably bears
a layer of reflective material, and/or of a material with a lower
refractive index, on its non-illuminated bounding edges 102 and on
one or more of its faces 112. Areas 114 on the face(s) 112 of the
sheet 100 can then be made to emit light by disrupting internal
reflection at these areas 114, as by roughening their surfaces,
removing any reflective layers, adding colorants or other
less-reflective material, or otherwise preparing these areas 114
such that the light within the sheet 100 tends to emit at these
areas 114 to a greater extent than at surrounding areas.
Alternatively or additionally, areas 114 of the sheet 100 can be
treated to fluoresce in response to some or all of the wavelengths
of light provided to the sheet 100, such that these areas 114 will
appear to be illuminated.
[0008] Further advantages, features, and objects of the invention
will be apparent from the remainder of this document in conjunction
with the associated drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIGS. 1A-1C present schematic views of a flexible
translucent sheet 100 having legs 106 (in FIG. 1A) which are folded
into stacked/overlapping sets (in FIG. 1B, and also in FIG. 1C) to
define input areas 116 at which light may be input from one or more
light sources 110 to cause emitting areas 114 to emit light.
[0010] FIG. 2 is a schematic view of a flexible translucent sheet
200 showing an arrangement similar to that of FIGS. 1B-1C, wherein
the legs 206 of sheet 200 are folded at bends 208 to define an
input area 216 for a light source 210.
DETAILED DESCRIPTION
[0011] Expanding on the discussion given in the foregoing Summary,
the sheets used in the invention may have any appropriate form. The
sheets preferably have at least substantially uniform thickness
(with thickness often being between 0.025 mm to 0.5 mm thick), and
preferably bear the aforementioned layers of reflective and/or
lower refractive index material on one or more of their surfaces
(most preferably on at least their opposing major faces). If legs
are formed in a sheet, the legs are preferably cut using a method
which leaves cut edges which are as optically smooth as possible to
promote efficient internal reflection at these edges. Stamping or
cutting with very sharp and/or heated blades, or using laser
cutting or another form of thermal cutting, can promote smoothness.
Other forms of cutting, e.g., water jet cutting, can also provide
acceptable results. Polishing can occur after cutting to further
promote smoothness, and such polishing can be performed
mechanically (e.g., with abrasives), thermally (e.g., by surface
melting), and/or chemically (e.g., by application of caustics).
[0012] The invention can be generated without forming legs in the
sheet, as by pleating/folding one end of a sheet to form a stacked
light input area, and leaving the other end of the sheet unfolded
to define the body to be illuminated. However, such an arrangement
can be bulky in comparison to the arrangements shown in the
drawings. One can choose among arrangements with or without legs,
or may combine features of these arrangements, to achieve an
arrangement which best fits the space requirements for the
application at hand. Any pleated areas, stacked legs, or similar
arrangements can be mechanically urged together, melted together,
and/or adhered together (preferably with an adhesive having the
same index of refraction as the sheet, or a lower one so as to
serve as a reflective layer) for ease of handling, and potentially
for better coupling efficiency at the light input area.
[0013] It is notable that where sheets are folded/bent, the
folds/bends are preferably such that they do not generate an
immediate 180 degree change in direction of a sheet, but rather
they have some radius of curvature. This helps to promote more
efficient internal reflection, and additionally some films can
"craze" (i.e., whiten or otherwise introduce a scattering haze) if
overly stressed by a sharp bend. Preferably, the radius of
curvature of a bend/fold will be at least ten times the thickness
of the film, with greater radii of curvature helping to reduce the
possibility of light loss. Radii of curvature of 75 times the
thickness of the film or less are useful for providing acceptable
light losses versus the space required for accommodating the
gradual folds/bends. However, if space or other considerations make
sharp bends/folds preferable, light loss can be reduced by applying
reflective and/or low refractive index cladding layers at the
folds/bends, and/or by treating sheets to reduce stress when they
are being folded/bent (as by heating sheets to become more
plastic). Any folds/bends that are made in the sheets need not
redirect legs into directions perpendicular to their axes, as shown
in the examples of FIGS. 1 and 2, and folds can instead (or
additionally) be made at different angles (e.g., to redirect legs
along angles oriented 45 degrees to their original unfolded
states).
[0014] The use of flexible sheets as lightguides provides many
advantages over the use of rigid sheets. The invention's
improvement in light-coupling efficiency and cost is particularly
pronounced at sheet thicknesses below 0.25 mm, which is
approximately the size of average LED and laser diode chips
suitable for use in edge lighting applications. Thus, below 0.25 mm
sheet thicknesses, it becomes particularly difficult and/or
expensive to generate arrangements for efficiently coupling light
into the sheet edge from a chip because of etendue and
manufacturing tolerance limitations. Further, since the sheets of
the invention are flexible, the sheets can shape to surfaces (e.g.,
a window surface) without appreciably changing in a surface's
shape, thickness and/or appearance, and they can deform as needed
(including during use, e.g., an illuminated sheet may wave in the
air, and/or during storage, e.g., a sheet can be rolled or folded
when not in use). Such flexible sheets are also typically less
expensive, thinner and lighter, and easier to store and machine
than rigid sheets, assisting in reduction of material, fabrication,
storage and shipping costs. Rolls of appropriate sheet material are
readily available with widths up to 20 feet (6 meters), and with
lengths of thousands of feet/meters, allowing the production of
very large sheets where desired (e.g., for billboards or other
large signage). Since flexible films are used in many industries,
many providers of sheet treatment services (e.g., cutting and
coating/laminating services) are available. Additionally, many film
manufacturers can accommodate coextrusion of films bearing from two
to hundreds of layers, and/or coating of films, so it is relatively
easy and inexpensive to generate sheets having different layers
which decrease light loss and/or otherwise promote internal
reflection.
[0015] The light source may be any suitable light source noted in
this document, and may take any other suitable form as well. Such
light sources may be directly coupled to the light input area
(i.e., the overlapping edges of the sheet), or may be coupled via
an intermediate lightguide, such as an optical fiber (or bundle)
which provides the light from the light source to the light input
area. The light sources need not emit visible light, and they might
interact with the light-emitting areas of the sheet to emit visible
light at these areas. More than one light input area can be
provided on a sheet (and multiple light sources can be used); for
example, two or more sets of the legs shown in FIGS. 1-2 might be
provided on opposing or different bounding edges of a sheet, and
each might be supplied with light from a different light source (or
from the same light source, if the stacked legs from each edge are
bent/folded to route to the same light source). In similar
respects, multiple sheets can be provided with light from the same
light source, as by having the same light source illuminate the
stacked legs of more than one sheet. If desired, the legs from the
separate sheets can be stacked together, perhaps in interleaved
fashion. Legs need not be folded and stacked in an orderly manner,
and multiple legs could simply extend outwardly, and then be
gathered in a disorganized bundle to have their bounding edges
stacked in random order. Stacking need not have all edges situated
in a linear array, and legs could, for example, be stacked
side-by-side in addition to being stacked top-to-bottom, such that
the input area presents a two-dimensional array of leg ends.
[0016] To illustrate an exemplary construction of the invention in
greater detail, a 0.01 inch (0.25 mm) thick and 48 inch (122 cm)
wide roll of BPA (bisphenol A) polycarbonate film was used to
construct illuminated sheets. The sheet had a yellowness index of
less than 0.54 measured using the ASTM D1925 standard. (The
yellowness index is related to the light absorption within the
sheet, and is preferably minimized to reduce absorption losses
and/or color shifting.) Similarly, the haze of the sheet was less
than 0.5% as measured using the ASTM D1003 standard. (Haze is a
value related to light scattering caused from imperfections on the
sheet surface and the existence of particles, air bubbles, or other
imperfections within the sheet's volume, and haze, like the
yellowness index, is also preferably minimized in the invention
where greater light transmission is desired.) In testing, this
material was found to allow high-quality light transfer, without
any significant degradation or color shifting, for approximately 8
feet (2.4 m) within the sheet, without significant color shifting,
when a broad band xenon illumination source was input at the edge.
At greater than 8 feet, color began to shift from white to red due
to uneven absorption of longer and shorter wavelengths, but
otherwise light intensity was substantially maintained for
approximately 20 feet (6 m) along the sheet with minimal light
leakage from haze.
[0017] The sheet was cut down into a 20 inch by 8 inch (51 cm by 20
cm) sheet using a #11 scalpel blade. Eleven legs having 10 inch (25
cm) length and approximately 0.73 inch (1.8 cm) width were cut
using #11 scalpel blades mounted in spaced relation on a bar
between two guiderails, such that the bar could be translated to
have the blades thereon cut the sheet beneath. After cutting the
slots, surface roughening and colorants were added to portions of
the roughly 10 inch by 10 inch (25 cm by 25 cm) body to frustrate
internal refection at these areas. Different methods for adding the
areas were used, such as sandblasting, surface scratching, and
inkjet printing of a light-scattering pigment. The legs were then
folded and stacked in a manner similar to that illustrated in FIG.
2. After stacking, the ends of the legs were cut using a heated
scalpel blade so that they better defined a smooth and continuous
light input area. The bounding edges of the legs partially melted
together during such cutting, enhancing smoothness and
continuity.
[0018] A green solid-state light source, more specifically a
PhlatLight PT120 offered from Luminus Devices, Inc. (Billerica,
Mass., USA), was then coupled to the light input area. The light
traveled down the legs into the unfolded body area, and scattered
at the treated areas, causing them to glow/illuminate. Some light
loss/scattering also occurred at the edges of the legs and unfolded
body area owing to the surface roughness of the cut edges. This was
reduced by polishing the surfaces of the sheet edges using
methylene chloride vapor polishing so that more optically smooth
edges were generated. Illumination also improved with better
coupling of the light source at the input areas, as by placing the
light source within a reflective shroud so concentrate the emitted
light onto the input area, and with polishing of the input area
(with flame polishing being used).
[0019] To illustrate another exemplary construction of the
invention, a roll of BPA (bisphenol A) polycarbonate film having
0.01 inch (0.25 mm) thickness was coated with a 2-10 micrometer
thick cladding layer of material having a lower refractive index
using a sheet coater. The chosen cladding material was the TC106
coating from Sun Process Corporation (Mt. Prospect, Ill., USA). The
cladded film was then stamped into smaller sheets with predefined
legs. A stack of sheets was placed in a methylene chloride vapor
etching chamber to simultaneously polish their edges. Areas of the
sheets were scraped to remove their cladding so that these areas
would later illuminate when light is supplied to the sheets. The
legs of each sheet were then folded so that their bounding edges
were aligned in stacked relationship to provide a light input area.
When a light input area of a sheet was illuminated in the manner
discussed above, the treated areas lit up brightly, and when the
illumination was removed, the treated areas were barely
visible.
[0020] The illuminated sheets provided by the invention have
numerous applications. Following are several examples.
[0021] Initially, there are numerous general illumination and
backlighting applications. General home and office lighting could
be provided by applying sheets to ceilings or walls, and the
flexibility of the sheets can usefully allow them to be applied to
non-planar surfaces. Since the sheets can accept high-intensity
point sources of light and disperse the light over a wide area, the
sheets offer a useful means for adapting LED lights--which are
often too intense for general home/office illumination, and which
require diffusion for comfortable viewing--for use in general
illumination.
[0022] The sheets are also highly useful for use in illuminated
signs, graphics, and other displays. Since a sheet can be installed
on a wall or window without significantly changing its appearance,
with the light-emitting area(s) becoming visible when the light
source(s) are activated, the invention allows displays to be
located at areas where typical displays would be aesthetically
unacceptable (e.g., on windows). The sheets may also be used in
situations where space considerations are paramount, e.g., when
lighting is desired within the ice of skating rinks (as discussed
in U.S. Pat. No. 7,237,396, which also describes other features and
applications that could be utilized with the invention). The
flexibility of the sheets allows them to be used in lieu of the
curtains sometimes used for climate containment, e.g., in the film
curtains that are sometimes used at the fronts of grocery store
freezers to better maintain their internal temperatures. The
flexibility of the sheets also allows their use in displays that
move, e.g., in flags that may move in the breeze.
[0023] The sheets can be used for backlighting or frontlighting
purposes in passive displays, e.g., as a backlight for an
illuminated advertising poster, as well as for active (changing)
displays such as LCD displays. Such applications generally require
compact, low-cost white-light illumination of consistent brightness
and color across the illuminated area. It is cost-effective and
energy-efficient to mix the light from red, blue, and green LEDs
for this purpose, but color mixing is often problematic. However,
with the invention, red, blue, and green light sources can all be
input into each stack of legs/input areas, and by the time the
light reaches the sheet, it will be sufficiently mixed that it
appears as white light. The light sources can be geometrically
situated, and adjusted in intensity, to better provide uniform
intensities and colors across the body. A similar arrangement can
be attained by providing stacked sheets (more specifically stacked
sheet bodies) wherein the colors in the sheets combine to provide
white light. Since some displays are provided on flexible
substrates--for example, "E-ink" thin-film displays on printed
pages--the sheets provide a means for allowing backlighting while
maintaining the flexibility of the display's media.
[0024] It is also notable that the invention has utility when
operated "in reverse"--that is, the light-emitting face(s) of a
sheet could be used as a light collector, with the sheet collecting
light and transmitting it through the legs to a photosensitive
element. As an example, sheets in accordance with the invention
could collect incoming light and internally reflect it to direct it
to a photovoltaic device for solar energy collection purposes. Such
an arrangement can also be useful for environmental
monitoring/sensing purposes, in that the sheet can detect and
collect light across a broad area, and the detector(s) at the legs
will then provide a measurement representative of the entire area.
A sheet could perform light collection of this nature in addition
to light emission. For example, in lighting applications, a sheet
might monitor ambient light, and then might be activated to emit
light once twilight or darkness is detected. Usefully, since it is
known that LEDs can also be "run in reverse"--that is, they can
provide output current/voltage when exposed to light--if LEDs are
used as an illumination source when a sheet is used for light
emission, they can also be used as detectors when a sheet is used
for light collection.
[0025] This written description uses examples to disclose the
invention, including the best mode, and also to enable any person
skilled in the art to practice the invention, including making and
using any devices or systems and performing any incorporated
methods. The patentable scope of the invention is defined by the
claims, and may include other examples that occur to those skilled
in the art. Such other examples are intended to be within the scope
of the claims if they have structural elements that do not differ
from the literal language of the claims, or if they include
equivalent structural elements with insubstantial differences from
the literal language of the claims.
* * * * *